NASA's Curiosity is set to make its historic landing this coming Sunday, August 5. Once settled, the rover will get to work analyzing the Martian surface and atmosphere for signs that the planet was once capable of harboring life — or might be again. But what does it mean to search for "potential" habitability?

To help us better understand the inner workings of the rover, we spoke to geobiologist Roger Summons, a professor at the Massachusetts Institute of Technology and an expert on the chemical signals of ancient life. He spoke to us about how the rover will be able to do many of the things that a real field scientist would do when evaluating a particular area for life.

Summons made it clear right from the outset that Curiosity is not capable of detecting life on Mars — nor is it meant to.

Instead, its job is to evaluate the Martian landscape and atmosphere for its potential to harbor life at some point in the planet's past.

In other words, it'll be evaluating Mars for its habitability.

"We know that life has existed on Earth for the past 3.5 billion years," Summons said, "but the signs of life are both rare and cryptic — not things like trilobites, leaves, or dinosaur bones — they're instead very subtle textures in rock and chemical signatures." Curiosity will be doing basic geochemistry looking for these signatures. He added, "Once we have more geologic information, then we can start to make valid hypotheses about the early conditions for life on Mars." To get this information, Curiosity is set to explore some of the oldest surface areas on Mars with its cameras and spectrometers.

Let's take a closer look at what these tools can do.

Cameras

Of Curiosity's three cameras, two will be put to work for geobiological purposes.

The rover's Mastcam will be capable of taking stereo color images and color video footage of the Martian terrain — and as per usual, NASA scientists will be able to stitch together those wonderful panoramic views of the landscape. In addition to pleasing those of us back home, this camera will also help the scientists to visually survey the landscape and various objects (like rocks) for signs of habitability.

Curiosity also has a camera mounted on one of its arms. This imager will allow scientists to take a closer and targeted look at rocks to see textures, structures, and colors. Specifically, scientists want to look for evidence of layering in rocks. "These sorts of things give you clues about whether or not the materials in these rocks are being transported by air or water," said Summons, "these factors will have different impacts on habitability."

And clearly, any evidence of water (both past and present) holds serious implications for any assessment of life. "All life requires water," noted Summons, "therefore evidence for the presence of liquid water is crucial — so we'll be looking for signs of the transport of sediments and minerals."

Spectrometers

Curiosity's spectroscopic arsenal is impressive.

Its primary tool is the Sample Analysis at Mars (SAM) system which takes up half the payload on board the rover. It's a suite of three different instruments, including a mass spectrometer, gas chromatograph, and tunable laser spectrometer.

SAM will look for and measure lighter elements such as hydrogen, oxygen, and nitrogen — elements that are associated with life. The mass spectrometer will separate elements and compounds for identification and measurement, while the gas chromatograph will heat soil and rock samples. As for the laser spectrometer, it will measure the abundance of various isotopes of carbon, hydrogen, and oxygen in atmospheric gases such as methane, water vapor, and carbon dioxide.

And yes, like the true field geologist that it is, Curiosity will be doing some of its own chemical analysis right there on the spot. After taking samples, it will conduct different experiments on rocks, such as heating them gently to evolve different gases, such helium and argon. "By doing so you can infer the age of rocks," said Summons, "and you can constrain timescales in this way — particularly with argon."

In addition to SAM, Curiosity is equipped with the Alpha Particle X-Ray Spectrometer (to measure the abundance of chemical elements in rocks), the ChemCam (which will analyze rocks and soils from a distance by using lasers), and the Chemistry and Mineralogy X-Ray Diffraction/X-Ray Fluorescence Instrument (which will identify and measure abundances of various minerals on Mars).

Curiosity's lasers will be able to query rocks from a distance of nearly 10 meters. "The laser can vaporize a small amount of rock in order to measure its particular spectrum and depict the bands for diagnostics of particular elements," said Summons, "that way we can get a better understanding of mineral compositions in the rock."

Looking for clues

Currently, geologists know that Mars is covered in basalt, which is part of the normal weathering process. But what they're really interested in knowing is if Mars has anything like clay minerals or calcium carbonate — remnants that would be more closely associated with biological processes.

"We're really hoping to find signs of water movements that could carry materials and create concentrations of things like organic matter which we could then query for signs associated with the conditions for life," said Summons.

Curiosity will also be measuring the atmosphere for spectral signatures, namely methane. In fact, as Summons told us, definitive proof that methane exists on Mars would be an incredibly powerful indication that the planet was once habitable.

"Methane has a limited lifetime — about hundreds of years with a planet like Earth, "he said, "so there has to be a source for methane, and it's typically organic life like bugs." So if methane is detected on Mars — and Summons is very dubious about this — the big question will be, where did it come from?

Looking at all this equipment, it's clear that NASA has done a great job preparing its robot geologist for the mission. Fingers are crossed that the landing goes well on Sunday.